The use of natural-appearing materials such as slate or wood shake for composite shingles is a very established practice in building construction. These natural materials are coveted for their appearance and material properties. However, the use of natural materials often has drawbacks that make them less desirable and uneconomical for many applications in modern building construction. Natural slate is coveted for its appearance and durability; however, slate is a very heavy building material with high material and installation costs. The material cost for slate shingles is much greater than the standard asphalt shingles used in most residential construction and its use in certain applications is nearly cost prohibitive. In addition to the higher material price, slate shingles have high installation costs because the shingles must be hand nailed due to the tendency of slate to chip or split under the impact of a nail driven by a pneumatic nail gun. To further add to its disadvantages, slate shingles are much heavier than asphalt shingles. Traditional roof construction may not always be adequate to support the weight of slate shingles; as a result, the structure supporting a slate roof must be stronger to accommodate the increased loads. The increased design load associated with slate shingles ultimately increases entire structure costs as the extra load in the roof must be carried all the way down to the foundations.
Wood shake shingles are similar in weight to common asphalt shingles and do not require increased structure costs; however, wood shingles also have some competitive drawbacks in modern construction. Wood shingles do not have an equivalent life span to asphalt shingles; thus, they need to be replaced much sooner. Further, wood shingles are typically more expensive than asphalt shingles thereby increasing the up front material costs. Wood shingles without sufficient sun exposure are subject to the growth of moss and subsequent rot. Wood shingles also absorb water which results in a tendency to curl and not remain flat on the roof. Wood shingle roofs require frequent “conditioning” wherein rotten shingles are identified and replaced. All of these factors result in increased maintenance costs. Further, wood shingles do not have the fire resistance of asphalt shingles and, in fact, may create a fire hazard as wood shingles are often dry and can actually accelerate a fire if an errant airborne cinder lands on the roof.
Because of the aesthetic appeal of slate and wooden shake shingles, light weight composite shingles made to resemble slate and wooden shake shingles have been developed. Advancements in composite materials have made it possible to manufacture composite shingles that are colored and textured to realistically imitate slate or wood shake shingles. Composite shingles have many advantages over shingles made from natural materials. Composite shingles are lighter in weight and allow a homeowner to obtain the look of slate while maintaining the structural load and framing requirements for a roof with traditional asphalt shingles. Composite shingles will not rot and often have at least a fifty-year life span resulting in low maintenance costs during a roofs life span. Some composite shingles can be installed using a pneumatic nail gun to reduce installation costs. For someone seeking the look of a slate roof, without the associated high cost of materials and installation, composite shingles have great appeal. Likewise, a consumer desiring the look of wooden shake shingles but with lower maintenance costs and increased life span, composite roof shingles have great appeal.
As the demand for composite shingles has increased, many improvements have been made to increase the performance of previous generations of composite shingles. Technologies improving the manufacturing efficiency allow composite shingles to be made with less material. In addition, alignment aids, such as laying lines, scales and spacing nibs, increase the efficiency of installation. However, known composite shingles still have performance defects. For example, when shingles include a cavity under the top surface to achieve a greater, more realistic height while still maintaining a low shingle weight, the top surface often deforms when the composite shingles sit in the sun for prolonged periods of time, thereby creating sag in the middle of the shingle or between the surface supports. Support rails are often added lengthwise within the cavity under the top surface for support in an attempt to remediate this problem; however, while support rails helped reduce the sag in the middle previously experienced, sag between the support rails is still present. In addition, by only including lengthwise support rails, the shingle is still vulnerable to buckling upon application of an uplift force load due to wind loads. In an attempt to adequately resist uplift forces, these rails must be thick to prevent buckling which increases the amount of material required and thus the overall weight of the shingle.
A need exists to increase the performance and efficiency of the structural design of composite shingles with a thick butt end and a formed cavity below the top surface all the while meeting the manufacturing and material constraints of the industry. Improvements of the present invention reduce or maintain the amount of material used in manufacture while simultaneously maintaining or increasing the performance of composite shingles.